Propeller Blade-Tip Flow Isolator

ABSTRACT

A propeller blade-tip flow isolator that can be used on a propeller, rotor, or wind turbine is provided. The propeller blade-tip flow isolator integrates with the blade at the outer radius and shields the propeller blade-tip boundary layer, reducing blade-tip vortices. A twist along the blade-tip chord further reduces or eliminates the blade-tip vortices that inherently occurs on the exposed blade tips during normal operations. Efficiency and performance are improved while noise and acoustic levels are reduced.

CROSS REFERENCES

This application claims priority to U.S. provisional patent application 62/238,135, filed 7 Oct. 2015.

BACKGROUND

Propellers are mechanical devices used to convert rotational shaft power into thrust and propulsion on a wide range of applications such as aircraft, drones, UAV's, ships, boats, submarines, and submersibles. On large ships, propellers are also referred to as “screws”. Wind turbines convert the kinetic energy from wind into rotating shaft power, which is usually converted into electrical power. Helicopters and tilt rotor aircraft use rotors for lift and propulsion.

Propellers, rotors, screws, wind turbines, and other rotating mechanical devices that convert rotating shaft power to or from a fluid share the same structure. The geometry and blade count vary based on the specific application, but they are all rotating mechanical devices with two or more attached angled blades and are herein referred to as “propellers”. Propellers can operate on compressible or incompressible fluids and are used in a wide range of applications.

FIG. 1A shows a generic propeller that can be used for propulsion on an aircraft, UAV, drone or wind turbine. Boats, ships, submarines and other water-based applications typically use a propeller with a higher maximum blade width to propeller blade radius ratio than air and wind based applications. The maximum blade width commonly occurs in the middle blade radius region and tapers to a minimum blade width at the blade tip, as shown in FIG. 1B.

FIG. 1C shows a sectional view looking down the blade axis away from the axis of rotation. The blade cross section and a typical fluid boundary layer outline are shown. The blade leading edge and the blade trailing edge are also shown. The blade chord is a line from the blade leading edge to the blade trailing edge and the blade pitch angle is the angle between the blade chord and the propeller's plane of rotation, which is a plane perpendicular to the propeller's axis of rotation.

Propellers all share the same disadvantages: fluid from the high-pressure blade surface can slip around the blade tip towards the low-pressure blade surface, generating non-axial fluid flow components and blade-tip vortices. These vortices spin off each blade tip in a helical shape, tracing the blade-tip path through the fluid stream. Non-axial fluid flow components, swirls and vortices are undesirable features, as they reduce the efficiency of a propeller's conversion of rotational shaft power to axial fluid flow that can be used for thrust. Non-axial fluid flow components also generate unwanted sound and acoustic signatures. These features also reduce the efficiency when converting the kinetic energy from a fluid stream into rotational shaft power.

FIG. 1D is a sectional view of a propeller blade cut along the blade axis, looking down the blade chord towards the blade trailing edge, showing the unobstructed fluid flow path between the high-pressure and low-pressure boundary layers.

To reduce blade-tip vortices generated by exposed blade tips, many blades are designed with the maximum blade width in the middle region of the blade radius, decreasing radially outward to a minimum width at the blade tip, as is shown in FIGS. 1A and 1B.

Reducing the propeller blade width radially outward towards the blade tip also introduces several disadvantages. The blade tip region experiencing the highest fluid velocity is reduced in effective thrust area, while still introducing drag. This also results in pressure profiles and boundary layers that vary radially outward from the axis of rotation towards the blade tip, which contributes to non-axial fluid flow components and blade-tip vortices.

The paradox with blade design is that a reduction in blade width towards the blade tip to overcome undesirable blade-tip vortices also results in increased non-axial fluid flow components, which contributes to blade-tip vortices. Blade designers expend great effort to understand the application and operating range for a specific propeller application. A variety of algorithms, computational fluid dynamics, and other complicated methods are used to design a propeller geometry optimized for a specific propeller application.

PRIOR ART

One way to eliminate blade-tip vortices is to contain the blades within an enclosed barrier or shroud, resulting in a ducted flow application such as a gas turbine or jet engine nacelle. The blade tip designs for ducted fluid flow applications in the prior art are designed to reduce blade tip leakage, reduce blade tip wear, provide blade tip cooling, or perform other functions not related to the present invention. The present invention provides a simple solution to reduce blade-tip vortices without the enclosed barrier, additional parts, and systems associated with ducted flow applications.

Vortex generators create vortices along the blade surface to affect the boundary layer and increase efficiency. The present invention reverses the blade-tip vortex at the blade tip, induces a reversed vortex, and is different from the vortex generators that are implemented along the blade surface.

U.S. Pat. Nos. 9,039,381, 8,038,396, 7,927,078, and U.S. Patent Applications 20160222941 and 20160177914 utilize vortex generators on the blade surface and are different from the present invention.

U.S. Pat. No. 8,690,536 uses a vortex generator to reduce the blade tip leakage in a ducted turbine application. The non-rotating enclosed barrier is used to block the blade-tip vortices, unlike the present invention, which provides a simple alternative to the enclosed barrier required for ducted flow applications.

U.S. Pat. Nos. 6,948,906 and 4,596,512 use internal passages inside the blade, allowing fluid to exit the blade tip face. The present invention does not contain passages and does not allow fluid flow out of the blade tip face.

U.S. Patent Application 20150247411 uses internal passages as vortex generators to reduce the leakage in a ducted fluid flow application. The present invention does not contain passages and does not allow fluid flow out of the blade tip face. The present invention also provides a simple alternative to the enclosed barrier required for ducted flow applications and is therefore not related.

U.S. Pat. Nos. 7,467,921, 6,749,152, 6,478,541, 5,735,670, 5,620,304, and 5,620,303 change the geometry of the blade during rotation, requiring additional means to affect these changes and are not related to the present invention, which uses a geometry that does not change during operation.

The outer most region of the blade to the blade tip is the largest contributing factor to blade-tip vortices. The prior art contains numerous variations in blade geometry moving radially outward from the axis of rotation towards the blade tip. Geometric blade variations inside of the blade-tip termination surface at the blade radius are not related to the present invention.

U.S. Pat. No. 5,788,191 uses a blade geometry that changes towards the blade tip along with triangular shaped vortex generators near the tip to increase performance or efficiency and is different from the present invention.

U.S. Pat. Nos. 9,085,359, 7,854,595, 7,513,750, 7,246,998, and 6,976,829 change the blade geometry by reducing the cord length and/or bend the blade moving radially outward towards the blade tip and are different from the present invention.

U.S. Pat. No. 6,761,539 changes the blade tip geometry by reducing the blade thickness towards the blade tip and is different from the present invention.

The blade tip region is subject to the most wear and damage. The prior art contains many replaceable blade tip solutions. The present invention can be implemented as a rigid continuation of the blade or attached using another desired method.

U.S. Pat. Nos. 9,399,919, 9,371,817, 7,771,173, 7,762,785, 7,758,312, and 8,647,068 use replaceable blade tips that also vary in geometry radially outward towards the blade tip and are unrelated to the present invention.

U.S. Pat. Nos. 5,885,059 and 5,320,494 present a blade tip material and process along with a geometry that varies radially outward towards the blade tip and are unrelated to the present invention.

U.S. Pat. Nos. 5,885,059 and 5,320,494 present blade tip material and process along with a geometry that varies radially outward towards the blade tip and are unrelated to the present invention.

Blade end-plate designs and blade tips with a 90-degree bend have been used to increase efficiency. However, they do not provide a complete barrier of the boundary layer at the blade tip and/or extend beyond the boundary layer protruding into the fluid stream. Unshielded regions of the boundary layer allow blade-tip vortices and undesirable fluid flow components to develop. Extending beyond the boundary layer into the fluid stream increases drag and adds extra unnecessary mass that increases the centrifugal and dynamic forces that must be accommodated by the propeller blade, shaft, and shaft bearings.

U.S. Pat. No. 9,366,224 presents a blade configured with a tip that splits along the blade plane into two rounded contours that connect to two winglets, one on the high pressure side and one on the low pressure side. This design contains rounded contours connecting the winglets to the blade body, unlike the present invention, which contains no rounded contours. The winglets and rounded contours extend well beyond the blade boundary layer into the fluid stream, increasing drag and adding extra mass, unlike the present invention which does not protrude into the fluid stream beyond the boundary layer. Additionally the present invention induces a reversed vortex to counteract the naturally occurring blade-tip vortices.

U.S. Patent Application 20160153424 presents a blade tip device with mountable means, unlike the present invention, which can be integrated rigidly at the blade tip, creating a continuous solid piece. The profile shape is triangularly arranged, creating a W shape which protrudes well beyond the blade-tip boundary layer, adding drag and mass. This differs from the present invention, which does not protrude out into the fluid stream beyond the boundary layer. Additionally the present invention induces a reversed vortex to counteract the naturally occurring blade-tip vortices.

U.S. Patent Application 20110070090 presents a blade tip configuration with a cylindrical tube facing into the fluid stream at the blade tip to counteract noise and blade-tip vortices. The counteracting swirl is generated inside the tube, which starts in the middle of the blade tip. This method uses a ducted cylindrical flow and differs from the present invention, which does not contain any internal flow components or means.

Advantages

Accordingly, several advantages of one or more aspects of the present invention when integrated with a rotating propeller blade tip are: to increase axial fluid flow components, to reduce fluid swirls and blade-tip vortices, to reduce acoustic levels, to improve efficiency when converting rotating shaft power to axial thrust, to improve efficiency when converting kinetic energy from a fluid stream into rotating shaft power, to simplify propeller blade designs, to provide more power transformation for a given propeller diameter. Other advantages of one or more aspects will be apparent from a consideration of the drawings and ensuing description.

Objective

It is therefore an objective of the present invention to provide a propeller blade-tip flow isolator derived from a propeller, rotor, or wind turbine blade tip geometry and boundary layer. The propeller blade-tip flow isolator shields the boundary layer on the high-pressure blade surface at the blade tip and the boundary layer on the low-pressure blade surface at the blade tip. With the boundary layers shielded at the blade tip, the fluid slippage around the blade tip is blocked reducing blade-tip vortices. When rigidly attached to a propeller, rotor, wind turbine, or other similar device higher efficiency is achieved when converting rotating shaft power into axial thrust or when converting kinetic energy from a fluid stream into rotating shaft power. Lower acoustic levels are also achieved. These advantages are further improved by introducing a twist along the blade-tip chord in the opposite direction to the vortex that inherently occurs along the blade tip during normal operations. These advantages can be achieved in a compressible or incompressible fluid application (such as air or water).

DETAILED DESCRIPTION

Propellers, rotors, wind turbines, and the like, herein referred to as “propellers”, are used in a wide range of applications, from generating axial thrust from a rotating shaft to converting kinetic energy from a fluid into rotating shaft power. Propellers can operate on compressible fluids (such as air) or incompressible fluids (such as water). The present invention provides methods and apparatus for increasing propeller efficiency by adding a blade-tip flow isolator to each propeller blade tip. The isolator shape is derived from the propeller blade-tip geometry and boundary layer outline. A twist is applied to the isolator along the curved blade-tip chord to further improve efficiency. In addition to improved propeller efficiency, acoustic levels are also reduced.

All the Embodiments presented herein are built for a counter-clockwise rotating propeller, looking down the axis of rotation upstream from the propeller. A counter-clockwise rotating propeller is herein referred to as normal operation.

In the prior art, the blade axis is shown as a line from the axis of rotation exiting the center of the blade tip. For the embodiments developed herein, a geometric blade axis is used, which further defines the blade axis as a line that intersects the center of the blade tip, intersects the propeller axis of rotation, and is perpendicular to the propeller axis of rotation. (On propellers with angled or curved blades, the geometric blade axis will not pass through the center of the blade body)

For the embodiments developed herein, two Cartesian coordinate systems and one cylindrical coordinate system are used. The first Cartesian coordinate system, herein referred to as (XYZ), has a Y axis parallel to the propeller's axis of rotation and pointing into the incoming fluid stream during normal operation. The Z axis is coincident with the geometric blade axis and points away from the propeller axis of rotation. The X axis points into the direction of rotation. The second Cartesian coordinate system, herein referred to as (X′Y′Z′), is the (XYZ) coordinate system rotated about the Z axis. The angle of rotation is the blade pitch angle at the blade tip. The resulting X′ axis is coincident with the flattened blade chord at the propeller blade tip. The origin of coordinate systems (X′Y′Z′) and (XYZ) is at the desired propeller blade radius, also referred to as Rint. The cylindrical coordinate system, herein referred to as (r″, θ″, z″), has a z″ axis coincident with the propeller axis of rotation and points into the receiving fluid stream. The origin is at the intersection of the axis of rotation and the geometric blade axis. Cartesian coordinate system (XYZ) and cylindrical coordinate system (r″, θ″, z″) are shown in FIG. 2A.

Each propeller blade tip must terminate into a cylindrical blade-termination surface, creating a required blade-tip end area. The Z axis of the cylindrical blade-termination surface is the propeller axis of rotation and the radius is the propeller blade radius, Rint.

The boundary layer outline over the blade-tip end area is also required. This boundary layer outline can be for a single operating condition or a combination of operating conditions. The prior art presents propeller blade-tip configurations with little or no blade-tip end area. FIG. 2A shows how a standard propeller can be modified by increasing the blade radius, then slicing the blade tips off at the desired propeller blade radius, generating the required blade-tip end area on the cylindrical blade-termination surface.

A Blade-Tip Leading Edge Point 2 is the blade leading edge on the blade-tip end area. A Blade-Tip End Point 7 is at the blade trailing edge on the blade-tip end area. The blade-tip chord is a line that starts at blade-tip leading edge point 2 and ends at the blade trailing edge point 7 on the blade-tip end area. A Blade-Tip Center Point 4 is centered on the blade-tip chord between the leading edge point 2 and the trailing edge point 7. Blade center point 4 is also the origin of both Cartesian coordinate systems (XYZ) and (X′Y′Z′). FIG. 2A shows a propeller with a cylindrical blade-termination surface, blade-tip chord, blade-tip end area, and blade-tip points 2, 4, and 7.

Embodiment 1

The blade-tip end area, boundary layer outline, blade-tip points 2, 4, and 7 are initially on the cylindrical blade-termination surface and must be flattened onto the two-dimensional xy plane of coordinate system (XYZ). If initially represented in cylindrical coordinates (r″,θ″,z″), the following equations will flatten and convert all points to coordinate system (XYZ):

x=θ″((2πRint)/360°) (where θ″ is in degrees)

y=z″

z=0 two-dimensional plane

The blade-tip end area, boundary layer outline, blade-tip chord, blade-tip points 2, 4, and 7 are now flattened and represented by coordinate system (XYZ) and must be transferred to coordinate system (X′Y′Z′) using a standard coordinate system rotation about the Z axis. The angle of rotation is the blade-tip pitch angle α. The following equations can perform the transformation:

x′=x cos(α)+y sin(α)+(Where α is the blade-tip pitch angle)

y′=−x sin(α)+y cos(α)

z′=z=0 (Axis of rotation)

The blade-tip end area, boundary layer outline, blade-tip chord, and points are now represented by coordinate system (X′Y′Z′), as shown in FIG. 2B. The blade-tip chord is now a straight line starting at leading edge point 2, passing through blade-tip center point 4, ending at blade end point 7, herein referred to as a straight chord. The pitch line is also a straight line extending from the straight chord. Two-dimensional is labeled 2D on many of the diagrams.

A two-dimensional isolator outline is developed as a curve, starting at leading edge point 2, as shown in FIG. 2C. The curve is initially between the blade-tip end area outline and the boundary layer outline, intersecting the low-pressure and high-pressure boundary layer outlines 10-20% down the straight chord, towards the blade-tip end point 7. The curve extends beyond the high-pressure and low-pressure boundary layer outlines until it is about 10% further from the straight chord than is each boundary layer outline. This occurs at the blade-tip center point 4. The curve flattens and generally follows the boundary layer outline, past the blade trailing edge at point 7, and is terminated by a line parallel to the y′ axis. This trailing edge termination line is at a pre-determined distance (labeled Isolator Pad) downstream of the blade-tip end point 7 along the negative x′ axis.

This termination line intersects the low-pressure isolator outline creating an Isolator Low-Pressure End 16, intersects the high-pressure isolator outline creating an Isolator High-Pressure End 18, and intersects the blade-chord x′ axis creating Isolator End Point 8. The completed two-dimensional isolator outline with all the points and references is shown in FIG. 2C. The isolator outline height is the maximum distance on the y′ axis from the high-pressure isolator outline to the low-pressure isolator outline. The Isolator Pad is a small distance of about 5% of the length of the blade tip chord.

The sharp corners of the isolator low-pressure end 16 and the isolator high-pressure end 18 are gently rounded. An Isolator Center-Point 6 is in the middle of the two-dimensional isolator outline on the x′ axis, half way between leading edge point 2 and end point 8, at x′=−(½)Isolator Pad. A line parallel to y′ at y′=−(½)Isolator Pad intersects the blade-tip end area outline, generating two points, which are used for geometric alignment between each propeller blade tip and the final blade-tip flow isolator. An Isolator Low-Pressure Interface Point 10 intersects the blade-tip end area on the low-pressure side of the blade-tip end area. An Isolator High-Pressure Interface point 12 intersects the blade-tip end area on the high-pressure side of the blade-tip end area. FIG. 2D shows the final two-dimensional isolator outline with points, outlines, axes, and labels.

A three-dimensional shape is generated by applying a pre-determined thickness to the two-dimensional isolator outline along the z axis. Half the thickness is applied inward along the z-axis. Half the thickness is applied outward along the z-axis, generating a flat plate with the two-dimensional x′y′ plane in the center, and bound by the isolator outline, shown in FIG. 2E.

The outer edge of this flat plate from leading edge point 2 to the isolator low-pressure end 16 is curved to minimize drag and reduce mass, creating an Isolator Low-Pressure Leading Edge 22. The outer edge this flat plate from leading edge point 2 to the isolator high-pressure end 18 is curved to minimize drag and reduce mass, creating an Isolator High-Pressure Leading Edge 24. The curved edges of the high-pressure leading edge 22 and low-pressure leading edge 24 merge together smoothly at leading edge point 2. The outer edge of this flat plate from the isolator low-pressure end 16 to the isolator high-pressure end 18 is tapered to minimize drag and reduce mass, creating an Isolator Trailing Edge 26. FIG. 2F shows cut X from FIG. 2E, showing the cross sections of the original flat plate, the curved leading edge 22, and the tapered trailing edge 26. FIG. 2G shows cut Y from FIG. 2E, showing the original flat plate and the curvature applied creating the leading edges 22 and 24. The resulting three-dimensional shape resembles an air foil designed to pass through a fluid with minimum drag and lift.

A set of points sufficient to define the surface of this three-dimensional shape is generated, creating an Isolator-Surface Point Set 28. A pre-determined twist angle is applied to the isolator point set 28 along the X′ axis. The twist is applied in the opposite direction to the blade-tip vortices generated on exposed propeller blade tips, as discussed in the prior art. The total angle of twist Ø, is evenly applied along the x′ axis. Half the total twist angle is applied at leading edge point 2 in the negative direction along the x′ axis. Half the total twist angle is applied at the isolator trailing edge point 8 in the positive direction along the x′ axis. The twist angle varies linearly between the leading edge point 2 and the trailing edge point 8 along the K axis and is represented by variable σ′. The following equation is used to calculate σ′ for every x′ value in isolator point set 28:

σ′=−((x′+(½)Isolator Pad)Ø)/Isolator Length

(where the Isolator Pad is the distance from point 7 to point 8 and the Isolator Length is the distance from point 2 to point 8 as seen in FIG. 2D.)

The twist is then applied using a standard coordinate system rotation about the X′ axis. The following equations are used to perform the rotation using variable twist angle σ′:

x2′=x′ (axis of rotation, unchanged)

y2′=y′ cos(σ′)−z′ sin(σ′) Where σ′ is variable function of x′

z2′=y′ sin(σ′)+z′ cos(σ′)

Every point in the isolator point set 28 is twisted by first determining the twist angle σ′ for ‘ each point, then applying the standard coordinate system rotation about the X’ axis using angle σ′ resulting in a corkscrew shaped isolator (represented by x2′,y2′,z2′). FIG. 2H shows a series of slices in the y′z′ plane that are twisted along the x′ axis. The x′y′ plane and a twisted surface resulting from twisting the x′y′ plane are also shown. Points 2, 4, 6, 7, and 8 are on the X′ axis and therefore not twisted. Points 10 and 12 are in the center of the twist and are not twisted. Points 2, 4, 6, 7, 8, 10, and 12 are herein referred to as an Isolator Reference Point Set 30.

Every point in the isolator point set 28 and the reference point set 30 are represented by the coordinate system (X′Y′Z′) and are transferred back to coordinate system (XYZ) using a standard coordinate system rotation about the Z axis. The angle of rotation is the negative blade-tip pitch angle −α. The following equations can perform the transformation:

x=x2′ cos(−α)+y2′ sin(−α)

y=−x2′ sin(−α)+y2′ cos(−α)

z=z2′ (Axis of rotation, unchanged)

All the points in the isolator point set 28 and the reference point set 30, now represented by coordinate system (XYZ), are curved and transformed to cylindrical coordinates system (r″,θ″,z″) using the following equations:

r″=Rint+z (Rint is the desired propeller radius)

θ″=x(360°/(2πRint)) (in degrees)

z″=y

This transformation curves all the points in isolator point set 28 creating a cylindrically curved airfoil surface uniformly twisted about the curved blade-tip chord. The isolator point set 28 is used to create a solid with a pre-determined rigid material, creating a Propeller Blade-Tip Flow Isolator, Embodiment 1. The resulting embodiment shields the fluid on the high-pressure blade surface from the fluid outside the blade tip. It further shields the fluid on the low-pressure blade surface from the fluid outside the blade tip, resulting in a configuration with reduced blade-tip vortices and reduced non-axial fluid flow components. The twist along the blade-tip chord further reduces or eliminate blade-tip vortices and further reduces non-axial fluid flow components.

FIG. 2I shows the original cylindrical blade-termination surface and the twisted cylindrical surface twisted along the curved blade-tip chord. A series of slices along the curved blade chord and the varying angles of twist σ′ are shown for each slice. The points in isolator reference point set 30 are on both the twisted surface and the original cylindrical blade-termination surface and can be used for alignment with the propeller on the required blade-tip end area.

All the points are represented in cylindrical coordinates (r″,θ″,z″) and can be transferred back to coordinate system (XYZ) using coordinate system transformations or the following equations:

x=r″ sin(θ″)

y=z″

z=r″ cos(θ″)−Rint (Rint is the desired propeller radius)

The connection between the propeller blade-tip flow isolator (embodiment 1) and each propeller blade tip occurs on the blade-tip end area which is common to the propeller and the propeller blade-tip flow isolator. Embodiment 1 is geometrically aligned with each propeller using leading edge point 2, blade-tip center point 4, interface point 10, and interface point 12. The connection between the propeller blade-tip flow isolator and each propeller blade tip should occur within the three-dimensional shape of embodiment 1 and the blade tip should terminate within the three-dimensional shape of embodiment 1. If any voids or gaps occur between the blade-tip end area and the inner surface of the embodiment 1, the blade tip should extend radially outward, through the inner surface of the embodiment 1, and terminate inside the three-dimensional shape of embodiment 1. If any portion of the blade-tip end area extends beyond the outer surface of embodiment 1, the blade tip should terminate at the outer surface of embodiment 1, leaving no protrusions.

FIG. 3A shows a propeller blade tip configured with embodiment 1, a propeller blade-tip flow isolator. FIG. 3B shows a view upstream of a propeller blade configured with a propeller blade-tip flow isolator (embodiment 1). The twisted corkscrew shape of embodiment 1 along the curved blade-tip chord, the location of sectional cuts 1, 2, 3, and FIG. 3C are also shown.

A sectional view looking away from the axis of rotation along the geometric blade axis from inside the propeller radius is shown in FIG. 3C. This view shows the boundary layer shielded by the propeller blade-tip flow isolator (embodiment 1). FIG. 3D shows a view looking down the geometric blade axis towards the axis of rotation, from outside the propeller radius. The locations of sectional cuts 1, 2, and 3 are also shown. These cuts are in a plane that is coincident with the propeller axis of rotation, z″.

FIG. 3E shows sectional cut 1, which is cut between leading edge point 2 and the blade-tip center point 4, looking towards the isolator trailing edge 26. FIG. 3F shows sectional cut 2, which is cut at the isolator center-point 6 and looking towards the isolator trailing edge 26. Isolator interface point 10 is just behind the cut plane and shown along with isolator interface point 12, which is immediately in front of the cut plane. (These interface points, while not on the cut plane, are very close to the cut plane and included to show where the alignment points are located, relative to the rest of the points in this cut.) FIG. 3G shows sectional cut 3, which is cut between isolator center point 6 and end point 7, looking towards the isolator trailing edge 26. FIGS. 3E, 3F, and 3G also show the twisting corkscrew nature of embodiment 1 along the curved blade-tip chord. FIG. 3H shows sectional cut 4, showing the tapered outline of the isolator trailing edge 26.

The pre-determined material and thickness used to create the propeller blade-tip flow isolator must be strong enough to handle static, dynamic, and transient structural loads, including centrifugal and aerodynamic loads, throughout the entire operating envelope and life-cycle of the propeller. The physical connection between each blade tip and the attached propeller blade-tip flow isolator occurs at or near the blade tip or as part of a continuous solid piece of material, and must be strong enough to handle static, dynamic, and transient structural loads including centrifugal and aerodynamic loads throughout the entire operating envelope and life-cycle of the propeller. Each propeller blade tip is integrated identically with an identical propeller blade-tip flow isolator, embodiment 1.

Embodiment 2

Embodiment 2 is a special case for embodiment 1, wherein no twist about the blade-tip chord is used creating a cylindrical version of the Propeller Blade-Tip Flow Isolator, Embodiment 2. The resulting embodiment shields the fluid on the high-pressure blade surface from the fluid outside the blade tip. It further shields the fluid on the low-pressure blade surface from the fluid outside the blade tip, resulting in a configuration with reduced blade-tip vortices and reduced non-axial fluid flow components. Embodiment 2 can be created using the same process used for embodiment 1, except that σ′=0, therefore no twist is applied along the x′ axis. FIG. 4A shows an orthographic view, looking down the axis of rotation of a propeller blade configured with embodiment 2. The curved edges of the high-pressure leading edge 22 and low-pressure leading edge 24 merge together at leading edge point 2. The curved cylindrical shape of embodiment 2, the tapered shape of the trailing edge 26, and the location of sectional cuts 1, 2, and 3 are also shown in FIG. 4A.

FIG. 4B shows sectional cut 1, which is cut between leading edge point 2 and the blade-tip center point 4, looking towards the isolator trailing edge 26. FIG. 4C shows sectional cut 2, which is cut at the isolator center-point 6, looking towards the isolator trailing edge 26. Isolator interface point 10 is just behind the cut plane and shown along with isolator interface point 12, which is immediately in front of the cut plane. (These interface points, while not on the cut plane, are very close to the cut plane and included to show where the alignment points are located, relative to the rest of the points in this cut.) FIG. 4D shows sectional cut 3, which is cut between the isolator center-point 6 and blade-tip end point 7, looking towards the isolator trailing edge 26. FIGS. 4B, 4C, and 4D shows the cylindrical shape of embodiment 2 along the curved blade-tip chord.

All Embodiments

All the Embodiments presented herein are built for a counter-clockwise rotating propeller, looking down the axis of rotation upstream from the rotating propeller during normal operation. A clockwise rotating propeller can be easily generated by changing the sign of θ″ in cylindrical coordinate system (r″,θ″,z″) or the sign of x in Cartesian coordinate system (XYZ).

Both embodiments of the propeller blade-tip flow isolator add additional volume outside the desired propeller blade radius, increasing the clearance radius and clearance volume of the modified propeller during operation.

Operation

For applications that convert rotating shaft power into axial thrust, the operation is the same as a standard propeller or rotor application. Applying shaft power results in propeller rotation, resulting in thrust along the axis of rotation, also referred to as axial thrust. For applications that convert kinetic energy from a fluid stream into rotating-shaft power, the operation is the same as a standard propeller/turbine application. Fluid flow relative to the propeller along the axis of rotation will induce propeller rotation, which can be converted into rotating-shaft power.

DRAWINGS

FIG. 1A shows a three-blade propeller used in an aviation or wind turbine application; prior art.

FIG. 1B shows a three-blade propeller used for thrust in a marine-based propulsion application; prior art.

FIG. 1C shows a sectional view of a propeller blade, looking outward from the axis of rotation towards the blade tip; prior art.

FIG. 1D shows a sectional view of a propeller blade, looking towards the trailing edge from a section cut along the blade axis; prior art.

FIG. 2A shows an orthographic view of a three-blade propeller with a cylindrical blade-termination surface and blade-tip end area.

FIG. 2B shows the cylindrical blade-termination surface flattened onto a two-dimensional plane, with the boundary layer outline and blade-tip end area.

FIG. 2C shows the two-dimensional isolator outline generated from the boundary layer outline and the blade-tip end area.

FIG. 2D shows the final two-dimensional isolator outline, points, labels and axes.

FIG. 2E shows an orthographic view of the flat plate isolator with cut x and cut y.

FIG. 2F shows a view of cut x from FIG. 2E.

FIG. 2G shows a view of cut y from FIG. 2E.

FIG. 2H shows an orthographic view of the isolator twisted about the x′ axis.

FIG. 2I shows an orthographic view of the twisted isolator curved along the cylindrical blade-termination surface, embodiment 1.

FIG. 3A shows an orthographic view of a propeller blade configured with propeller blade-tip flow isolator, embodiment 1.

FIG. 3B shows an orthographic view of a propeller blade integrated with a propeller blade-tip flow isolator; embodiment 1.

FIG. 3C shows a sectional view looking along the geometric blade axis (away from the axis of rotation) from inside the propeller blade radius.

FIG. 3D shows a view looking along the geometric blade axis (towards the axis of rotation) from outside the propeller blade tip.

FIG. 3E shows a sectional view of a propeller blade configured with a propeller blade-tip flow isolator, embodiment 1, looking towards the isolator trailing edge 26, at cut location 1.

FIG. 3F shows a sectional view of a propeller blade configured with a propeller blade-tip flow isolator, embodiment 1, looking towards the isolator trailing edge 26, at cut location 2.

FIG. 3G shows a sectional view of a propeller blade configured with a propeller blade-tip flow isolator, embodiment 1, looking towards the isolator trailing edge 26, at cut location 3.

FIG. 3H shows a sectional cut from FIG. 3G showing the isolator trailing edge 26.

FIG. 4A shows an orthographic view (looking down the axis of rotation) of a propeller blade tip integrated with a cylindrical propeller blade-tip flow isolator, embodiment 2.

FIG. 4B shows a sectional view of a propeller blade configured with a cylindrical propeller blade-tip flow isolator, embodiment 2, looking towards the isolator trailing edge 26, at cut location 1.

FIG. 4C shows a sectional view of a propeller blade configured with a cylindrical propeller blade-tip flow isolator, embodiment 2, looking towards the isolator trailing edge 26, at cut location 2.

FIG. 4D shows a sectional view of a propeller blade configured with a cylindrical propeller blade-tip flow isolator, embodiment 2, looking towards the isolator trailing edge 26, at cut location 3.

REFERENCE NUMERALS

-   -   2 Blade-Tip Leading Edge Point     -   4 Blade-Tip Center Point     -   6 Isolator Center Point     -   7 Blade-Tip End Point     -   8 Isolator End Point     -   10 Isolator Low-Pressure Interface Point     -   12 Isolator High-Pressure Interface Point     -   16 Isolator Low-Pressure End     -   18 Isolator High-Pressure End     -   22 Isolator Low-Pressure Leading Edge     -   24 Isolator High-Pressure Leading Edge     -   26 Isolator Trailing Edge     -   28 Isolator-Surface Point Set     -   30 Isolator Reference Point Set 

1. A propeller blade-tip flow isolator comprising; a physical barrier isolating a high-pressure boundary layer from a fluid outside of a blade tip, the physical barrier isolating a low-pressure boundary layer from the fluid outside of the blade tip, providing means for reducing blade-tip vortices, further providing means for increasing axial fluid-flow components.
 2. Said propeller blade-tip flow isolator of claim 1, wherein said propeller blade-tip flow isolator is twisted along a blade tip chord in an opposite direction to a vortex generated by exposed blade tips, providing means to induce a vortex in an opposite direction than a naturally occurring vortex generated by exposed blade lips, whereby blade-tip vortices and non-axial fluid flow components are further reduced.
 3. A method for reducing propeller bladc-tip vortices comprising; a propeller blade-tip flow isolator derived from a propeller blade-tip end area and a propeller blade-tip boundary layer, twisted along a propeller blade-tip chord in an opposite direction of the propeller blade-tip vortices generated by exposed propeller blade tips, providing means to induce a vortex in the opposite direction than the naturally occurring vortex generated by exposed propeller blade tips, whereby propeller blade-tip vortices, non-axial fluid flow components, and noise are reduced. 